Phosphatizing operations carried on in water have typically provided drawbacks, including sludging and the need for a multistep operation, to achieve dry, coated articles. In an early attempt to overcome such problems, as described in U.S. Pat. No. 2,515,934, from 1 to 7% of the commercial phosphoric acid 85% syrup was used in an organic mixture, rather than in water. Representative of these mixtures was a 50/50 blend of acetone and carbon tetrachloride. With the blend, only a few steps were needed for phosphatizing.
In subsequently developed operations, a metal article for phosphatizing might be dipped in a chlorinated hydrocarbon degreasing solution, then come in contact with a non-aqueous phosphatizing solution, and thereafter be returned to the chlorinated hydrocarbon degreasing solution for a final rinse operation. Such operation has been described for example in U.S. Pat. Nos. 3,100,728 and 3,197,345. As also discussed in the U.S. Pat. No. 3,197,345, it was becoming recognized that there was a water-based process, also called an "aqueous" method of phosphatizing metal articles, and on the other hand a solvent-based process, which was therein noted as the "dry" process. The latter process typcially employed a solution of phosphoric acid in a chlorinated hydrocarbon solvent. Since the compositions of the U.S. Pat. No. 3,197,345 relied on chlorinated hydrocarbons, the phosphatizing method used was the "dry" process and the useful compositions were substantially water-free compositions.
Special organic phosphate complexes could be useful in the non-aqueous solutions. They had the advantage of providing protective coatings of enhanced corrosion resistance. This approach was taken in U.S. Pat. No. 3,249,471. Another approach to the dry process, or to the "non-aqueous" process as it was also called, and that was employed in U.S. Pat. No. 3,297,495, was the use of a high strength acid. In such patent, the acid used was preferably one of 96-100% phosphoric acid. This concentrated acid presented sludge problem, but these were overcome by employing special additives.
More recently, as discussed in U.S. patent applications Ser. Nos. 560,377 and 560,378, now U.S. Pat. Nos. 4,029,523 and 4,008,101, respectively, water resistant coatings have been achieved from organic phosphatizing compositions. Such compositions can be most desirably based on methylene chloride and further may contain a few percent or more of water without losing liquid phase homogeneity.
A variation in the prior art efforts involves the addition of a stabilizing agent to a coating bath to prolong the formation of adherent coatings from the bath. In West German Pat. No. 1,222,351, the use of an agent such as dimethyl glyoxime, as a stabilizer, has been shown. The baths, even with stabilizer, are of dubious quality without the use of commercial ethanol. This necessarily introduces a minor amount of water into the coating composition. However, emphasis is on higher boiling solvents, and even with commercial ethanol, resulting compositions can be dangerously flammable.